Hello newbphile,
I own both of those cans and both are great. As you most likely know the price difference is large, about $130 for the HD595s vs. $450-$500 for the HD650s. One thing Hi-end cans like the 650s will due is reveal a poor source 320kps mp3 through a n a/v receiver will probably leave you dissapointed, the HP circuit in most receivers are an afterthough by the manufacturer and not very good. Though I am sure it's much better than a stock soundcard. My reccomendation is similar to how I started out in this hobby. I would purchase the HD595s and take the difference in price of the 650s and improve your source. Get some software and rip your cd's into flac 24bit/96khz and get a entry level DAC/amp combo. Some examples; Fiio E7/E9 combo $199, Headroom total Bithead DAC/Amp $169, or something like the Grant Fidelity Tube DAC 09, it has a very good SS headphone amp built in as well as numerous inputs which would allow for expansion and upgrade. You can connect your computer using USB, optical or coax, and it is 24/96 compatible and has a tube buffer output stage as well. $240-$280. I have owned all of these at one time or another and was happy with all for their price points. Hope this helps!

I had the HD280 Pro a while ago and upgraded to the HD650 (amplified by a FiiO E7/E9) and the difference is absolutely massive. I've listened to a lot of high end headphones and I think the HD650 is the finest headphone under $1,000, period. If the price is ok, I would definitely suggest you try them. You can order them from headphone.com and send them back within 30 days if you decide you don't like them, I did that with 3 or 4 different headphones before I got the HD650 and fell in love.

You mean 44.1hz and 16bit sense there CD's? IF you get either Id suggest getting a NuForce DAC/amp.